A cardiac pacemaker is an electronic therapeutic instrument that is implanted in the body and employs a battery-powered pulse generator to deliver electrical pulses. The pulses are transferred via a lead to an electrode to stimulate the heart muscle to which the electrode is attached, resulting in the heart activation and contraction, achieving the treatment of heart dysfunction caused by some cardiac arrhythmia conditions.
A DDD pacemaker is able to sense and pace the atria and ventricles. However, improper pacing may cause some undesirable events.
An atrial pacing pulse delivered during the atrial vulnerable period may induce atrial tachycardia or other kinds of arrhythmia. This often takes place in the following two circumstances:
1. In a dual-chamber tracking mode such as DDD, it usually happens close to an atrial-sensed event within an atrial refractory period and is conventionally prevented by introduction of non-competitive atrial pacing (NCAP). In the DDD or DDDR mode, if this function is enabled, an atrial-sensed event within a refractory period will initialize an NCAP interval. If a scheduled atrial pacing event is to occur within the NCAP interval, then the scheduled atrial pacing event is delayed until the end of the NCAP interval. The delay in atrial pacing will impact the timing of ventricular events. Therefore, In order to maintain a stable ventricular heart rate, the paced atrioventricular (PAV) interval needs to be shortened.
However, with the conventional implementation, there is likelihood for an over-shortened PAV, a relatively great lower frequency limit, as well as a ventricular frequency lower than the lower frequency limit in case of a long atrial refractory period after ventricular pacing.
2. In a DVI or DVIR mode of conventional dual-chamber pacemakers, due to the absence of effective atrial sensing, the aforementioned issue may occur close to an atrial event within or not within an atrial refractory period and leads to severe tachycardia. Therefore, there is a need in the art for a novel medical device for treating cardiac arrhythmia, which can solve the problem of induced atrial tachycardia.